Are Ryan Gosling and Eva Mendes on the Rocks?

While Ryan Gosling promotes his directorial debut, Lost River, at the Cannes Film Festival this week, one person has been conspicuously absent: his girlfriend of three years, Eva Mendes – who happens to costar in the film.

Gosling, 33, hit the red carpet instead with Mad Men's Christina Hendricks, who also appears in the trippy movie, which is set in an urban wasteland.

Still, added Corliss, "give some credit to Gosling … for his mad mash-up of horror and social statement, crackpot fantasy and Sundance-style meandering." And Anne Thompson of Indiewire praised it as an "impressive impressionistic well-wrought debut."

Meanwhile, Mendes, 40, has been keeping a low-profile, and the pair haven't been photographed together since last November. But in February Mendes appeared to playfully shoot down breakup rumors, telling Ellen DeGeneres that her Valentine's Day plans involved "watching The Notebook or something."

Christina Hendricks and Ryan Gosling

KCS Presse / Splash News Online

The couple, who struck up a romance on the set of their 2012 drama The Place Beyond the Pines, have been tight-lipped about their relationship, but in February 2012 Mendes told Marie Claire that Gosling is "a dream costar," adding, "He's amazing."

And in May Gosling was photographed at the premiere of White Shadows wearing a necklace reading "Hugo" – the name of Mendes's beloved dog.